( Supported in part by NASA2-538 and NIH AR41452 to W. Landis) The shapes and orientation of mineral crystals and collagen fibers in avian and murine tendon and bone, and abnormally mineralized skin in rats, are being investigated as models for human disease and development by HVEM tomography. Initial studies focused on differences in structural details of collagen, non-collagenous matrix components, mineral and mineral-matrix interaction. Reconstructions made in the course of previous work at BMIRR provided basis for this work. A topographic reconstruction of a section of nanogold-labeled chick skull was made using the HVEM, to demonstrate that permeabilization techniques being developed permit the label to penetrate the cell membrane of the osteoblasts. Stereo pairs of thick sections of tibia and femur from an osteogenesis imperfecta (brittle bone disease) mouse treated with biphosphonate were recorded on the HVEM. Biphosphonate may be involved in mineralization repair by mineral-collagen reactions. We observed an interesting and unusual crystalline arrangement at the collagen/bone interface. We found what appeared to be a surface coating of mineral on the bone. Electron diffraction at 1.0 MeV did not reveal a different crystal structure from the bulk mineral, but showed possible orientation changes. We assisted Dr. Landis with preparation of thin-sections of tooth enamel, from which a tilt series was recorded at Harvard, and the reconstruction made here. We made four additional reconstructions from HVEM tilt series. The tilt-series images for these reconstructions did not have the gold markers we normally use for alignment, so we implemented a markerless alignment procedure. Dr. Landis visited the lab several times to do microscopy and to work with the tomographic reconstructions. Dr. Landis now has a SGI workstation and the SPIDER software in his lab, and we are helpng him learn how to do reconstruction and visualization of his tomogrrams. Landis, W.J., K.J. Hodgens, J.Arena, M.J. Song, and B.F. McEwen. (Late 1996) Structural relations between collagen and mineral in bone as determined by high voltage electron microscopic tomography. Microsc. Res. Tech., 33:192-202. Landis, W.J., K.J. Hodgens. (Late 1996) Mineralization of collagen may occur on fibril surfaces: evidence from conventional and high-voltage electron microscopy and three-dimensional imaging. J. Struct. Biol., 117:24-35. Landis. W.J. (Late 1996) Mineral characterization in calcifying tissues: atomic, molecular and macromolecular perspectives. Connect. Tis. Res., 34:239-246. Landis, W.J. (1997) Interactions of collagen and mineral in vertebrate tissues. Acta Metall. Mater. (in press). Landis WJ, Hodgens KJ, Berkery D, Owen CH. Localization of osteopontin in bone by immunocytochemistry in three dimensions. Fifth International Conference on the Chemistry and Biology of Mineralized Tissues. Connect Tissue Research 35:413, 1996. Landis WJ. Characterization of the nucleation and growth of mineral in organic matrices of vertebrate tissues. American Chemical Society 212:INOR 174, 1996.